SYNTHESES AND APPLICATIONS OF GOLD BASED NANOMATERIALS UTILIZING SELECTIVE METALS AS REDUCING AGENT

Abstract

The thesis entitled, “Syntheses and applications of gold based nanomaterials utilizing selective metals as reducing agent” has been divided into four chapters. Chapter 1: General introduction of Gold-metal oxide based nanocomposites, their properties and advantages as compared to their single counterparts. Synthesis and various applications has been also discussed. Anisotropic nanoparticles and impact of kinetic parameters on the morphology has been discussed in details. Recent advances in the synthesis of gold nanoprism and its applications have been summarized. Chapter 2: This chapter has been divided into two sections. The objective is to synthesize various gold-metal oxide nanocomposites using metal powder Zn(0) and Fe(0) as reducing agent. The synthesis scheme is based on the redox reaction between Au(III) and metal such as Zn(0) or Fe(0) where metal act as reducing agent as well as metal source. Section A describes room temperature synthesis of citrate stabilized Au-ZnO nanocomposites using Zn(0) metal powder as reducing agent in the presence of seed. The synthetic condition were optimized by varying seed concentration, sodium citrate, Zn amount and reaction time. Luminescent crystalline Au-ZnO nanocomposites were formed with prolonged stirring upto 150 min. Small size AuNPs were observed on the surface Au-ZnO nanocomposites with fluorescence spectra at around 496 nm. The luminescent property of the Au-ZnO nanocomposites were further applied for cell imaging and visible light induced photodegradation application. Section B describes the synthesis of PEG-SH stabilized Au-FexOy nanocomposites using Fe(0) metal powder as reducing agent. Au-FexOy nanocomposites were prepared by varying PEG-SH amount. The nanocomposites obtained were put for calcination in inert atmosphere at 800 °C for 8 hours. Flower shaped morphology obtained after calcination. The Au-FexOy nanocomposites showed excellent peroxidase activity with low Km values and comparable maximal velocity as compared to reported literature values. The peroxidase mimic activity shown by the nanocomposites was utilized for the colorimetric glucose detection. Chapter 3: This chapter has been divided into two sections. The objective is to develop new synthesis methodology for anisotropic gold nanoparticles utilizing redox reaction between Au(III) and Mn(0) metal powder in the presence of HCl as proton source. Section A describes seed free synthesis of polyethylene glycol stabilized gold nanoprism exploiting manganese metal at low pH. Kinetics were performed without seed varying HCl concentration, PEGSH, Mn and temperature. The synthesis was performed using different metals such as Zn(0), Fe(0) and Cr(0). Influence on the growth rate with varying reaction conditions were studied by fitting the time dependent absorbance data at 536 nm and 850 nm using KJMA model. The nanoprism formation and aggregation observed in TEM images was correlated with the growth rate and aggregation rate calculated using equation from KJMA model. HRTEM analysis was done to understand the growth mechanism for the nanoprism formation and crystal packing pattern. Nanoprism were synthesized on large scale using the optimized condition based on the kinetic studies and purification done using centrifugation. Nanoprism obtained were utilized for growth reaction in the presence of amine modified DNA and positively charged amino acids for edge selective and face selective growth respectively. Section B describes room temperature seed mediated synthesis of gold nanoprism in the presence of PEG-SH as stabilizing agent and Mn metal as reducing agent. Seed mediated synthesis were optimized by varying the temperature, Mn metal, PEG-SH, and seed concentration. Time dependent absorbance spectra were recorded for 6 hours varying seed concentration. TEM images confirmed the formation of nanoprism along with spherical seed. Chapter 3: This chapter has been divided into two sections. The objective is to develop new synthesis methodology for the synthesis of gold-manganese oxide nanocomposites utilizing redox reaction between Au(III) and Mn(0) metal powder. Section A describes the synthesis of Au-MnxOy nanocomposites using Mn metal as reducing agent in the presence of amino acid as stabilizing agent. The reaction were performed in neutral, acidic and basic condition using tryptophan as stabilizing agent. The reaction was performed using different amino acids as stabilizing agent and change in time dependent absorbance spectra was studied. Gold nanoparticles deposited on manganese oxide sheet observed in TEM images. The reaction condition was optimized by varying the Mn, tryptophan and seed concentration. Au-MnxOy nanocomposites were further utilized for superoxide dismutase mimic activity. The redox mediated synthesis between Au(III) and Mn(0) in presence of citric acid and amino acids was also tried at high temperature in autoclave. Gold nanoparticle particles formation observed along with manganese oxide sheet mixture observed in TEM images. Section B describes the synthesis of gold manganese oxide nanocomposites using Mn metal as reducing agent in the presence of PEG-SH as stabilizing agent in acidic medium. Optimization was done varying PEG-SH, Mn, HCl and seed concentration. Changes in the absorbance spectra were observed when the reaction performed in the presence of Mn metal powder as compared to gold seed. The formation of nanocomposites was confirmed using TEM analysis. Mn based reduction was also performed at high temperature and pressure using different stabilizing agent. The thesis ends with an overall conclusion and provides scopes for further research in this area.